Lightweight magnetic particle device

ABSTRACT

A multiple working surface magnetic particle device for transferring torque between two rotatable members is disclosed. The magnetic particle device includes relatively rotatable members defining a gap therebetween containing a magnetically reactive medium. The magnetically reactive medium stiffens in the presence of a magnetic field interlocking the rotatable members. The multiple working surface design allows for a reduction in the size and weight of the magnetic field source resulting in a more compact, lighter weight magnetic particle device.

RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 09/702,949, entitled LIGHTWEIGHT MAGNETIC PARTICLE DEVICE,filed Oct. 31, 2000 now U.S. Pat. No. 6,581,739, the disclosure of whichis incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to magnetic torque-transferringdevices and more particularly to those that employ a magneticallyreactive medium for coupling together two relatively rotatable members.

BACKGROUND OF THE INVENTION

Magnetic particle devices are known in the art. Generally, magneticparticle devices are based on electromagnetic and mechanical forces thatact on a magnetically reactive medium disposed between the workingsurfaces of a driven member and driving member. The magnetic forcesoperate to increase the viscosity of the medium to interlock the drivenand driving members. Magnetic particle devices are often designed asquick-acting electrically activated brakes or clutches for thetransmission of torque. Alternatively, magnetic particle devices may bedesigned to impart drag between rotatable surfaces to maintain tension.

Where magnetic particle devices offer many advantages, such as lowvibration torque transfer, the ability to operate in the slip condition,and the controllability of torque transfer over a relatively wide rangeof electrical input, there is a drawback as well. Conventional magneticparticle devices are relatively heavy due to the use of electromagnetsas the source of a magnetic field. Known electromagnets generallycomprise a shell with known magnetic properties and a coil of conductivewire. The thickness of the shell serves to define the working surfacearea of the device. Since the working surface is actually being coupleddue to the increased viscosity of the magnetically reactive medium, anefficient design is one that maximizes the working surface area.Unfortunately, to increase working surface area in a conventionaldevice, the thickness of the electromagnet shell must be increased,thereby undesirably increasing the weight.

Accordingly, there exists a need for a lightweight magnetic particledevice that does not compromise working surface area or reduce operatinglife. The present invention provides an effective lightweight magneticparticle device wherein the reduction in weight is achieved withoutsacrificing working surface area or adversely affecting the operativelife.

SUMMARY OF THE INVENTION

The present invention recognizes the disadvantages and limitationscommonly associated with the operation of conventional magnetic particledevices. By constructing a magnetic particle device in accordance withan aspect of the current invention, the weight of the magnetic particledevice can be significantly reduced without adversely affecting theoperating life of the device.

A multiple working surface magnetic particle device for transferringtorque between two rotatable members is disclosed. The magnetic particledevice comprises relatively rotatable members defining a gaptherebetween containing a magnetically reactive medium. The magneticallyreactive medium stiffens in the presence of a magnetic fieldinterlocking the rotatable members. In an embodiment of the invention,the rotatable members include include regions of relatively high and lowmagnetic permeability positioned to create multiple working surfacesthrough which magnetic flux weaves to activate the magnetically reactivemedium. The multiple working surface design allows for a reduction inthe size and weight of the magnetic field source resulting in a morecompact, lighter weight magnetic particle device.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and inventive aspects of the present invention will becomemore apparent upon reading the following detailed description, claims,and drawings, of which the following is a brief description:

FIG. 1 is a cross-sectional view of a magnetic particle device accordingto an embodiment of the present invention.

FIG. 1A is a cross-sectional view of a magnetic particle deviceaccording to another embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a magnetic particle gapaccording to the embodiment of FIG. 1, with no magnetic flux appliedacross the gap.

FIG. 3 is an enlarged cross-sectional view of a magnetic particle gapaccording to the embodiment of FIG. 1, with magnetic flux applied acrossthe gap.

FIG. 4 is an enlarged cross-sectional view of the interface of theelectromagnetic and the first and second rotatable members according tothe embodiment of FIG. 1, showing a path of the magnetic flux.

FIG. 5 is a cross-sectional view of another embodiment of a magneticparticle device.

FIG. 6 is a cross-sectional view of another embodiment of a magneticparticle device.

FIG. 7 is a cross-sectional view of another embodiment of a magneticparticle device.

FIG. 8 is an exploded view of the first and second rotatable members asdescribed in the embodiment shown in FIG. 7.

FIG. 9 is a cross-sectional view of another embodiment of a magneticparticle device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, an embodiment of a magnetic particle device 10 inaccordance with the principles of the present invention is shown. Thedevice 10 includes a stationary housing member 12 having a duct 14therethrough for receiving a rotatable shaft 16. Shaft 16 is rotatablysupported within duct 14 by bearings 18 and 20 the positions of whichare determined by shoulders 22 and 24 that are formed within duct 14 ofhousing member 12 and shoulder 25 formed on shaft 16. Bearing 18 isbiased against shoulder 24 by an annular retainer member 26. Bearing 20is biased against shoulder 22 by a biasing member (not illustrated) in adevice that is driven by the magnetic particle device 10.

A first rotatable member 30 of known magnetic properties is fixedlysecured to shaft 16. First rotatable member 30 includes a cylindricalportion 32 located radially outwardly of shaft 16 such that cylindricalportion 32 is substantially parallel with shaft 16. Cylindrical portion32 includes an inner surface 34 and an outer surface 36. Outer surface36 includes a plurality of grooves 38, depicted in the FIG. 1 asgenerally trapezoidal in cross-section, but not intended to be limitedthereto. Grooves 38 can also, in the alternative, be located on innersurface 34 or located on both inner surface 34 and outer surface 36 ofcylindrical portion 32, as seen in FIGS. 5 and 6 and explained infurther detail below.

A second rotatable member 40 of known magnetic properties is supportedon shaft 16 by a bearing 41, the position of which is determined by ashoulder 42 located on a distal end 43 of shaft 16 and a foot 44 offirst rotatable member 30. Second rotatable member 40 is positioned onbearing 41 by a shoulder 45 located on a base 46 of second rotatablemember 40. Base 46 further includes a plurality of teeth 48 for engagingthe underside of a typical drive belt (not illustrated) found inautomotive applications. While the present invention describes amagnetic particle device driven by a belt, it is understood that othersuitable mechanisms may be employed to drive the device.

Second rotatable member 40 further includes a cylindrical portion 50located radially outwardly of cylindrical portion 32 of first rotatablemember 30 and substantially parallel to shaft 16. Cylindrical portion 50further includes an inner surface 52 and an outer surface 54.

Inner surface 52 further includes a plurality of grooves 56, depicted inthe FIG. 1 as generally trapezoidal in cross-section, but not intendedto be limited thereto. Grooves 56 can also, in the alternative, belocated on outer surface 54 or located on both inner surface 52 andouter surface 54 of cylindrical portion 50, as seen in FIGS. 5 and 6 andexplained in further detail below. Grooves 56 are positioned on innersurface 52 such that grooves 56 are located radially outwardly of apoint equidistantly between grooves 38 in first rotatable member 30.Grooves 38 on cylindrical portion 32 and grooves 56 on cylindricalportion 50 define therebetween a plurality of working surfaces 58, 59,60 and 61. Working surfaces 58, 59, 60 and 61 cooperate with amagnetically reactive medium 64 (as best seen in FIG. 2) to interlockfirst rotatable member 30 and second rotatable member 40 whenmagnetically reactive medium 64 is subjected to a magnetic field.

First rotatable member 30 and second rotatable member 40 are not incontact, but define therebetween a uniform gap 66, generally toroidal inconfiguration. Gap 66 is of a predetermined width to permit a thin layerof magnetically reactive medium 64 (as seen in FIG. 2), such as amagnetically reactive powder, to reside therein. A magnetically reactivepowder is the preferred medium because it has the advantage of beingresistant to temperature levels that would degrade oil basedmagnetorheological fluids. Grooves 38 in first rotatable member 30 andgrooves 56 in second rotatable member 40 serve the purpose of providingadditional physical volume for receiving magnetically reactive medium 64when no magnetic field is applied. Removing magnetically reactive powder64 from gap 66 when no magnetic field is applied decreases frictionthereby reducing drag between first rotatable member 30 and secondrotatable member 40. In addition, grooves 38 and 56 aid in concentratingthe lines of magnetic flux 68 across gap 66 and substantially throughworking surfaces 58, 59, 60 and 61 as seen in FIG. 4.

As illustrated in FIG. 1, two non-contacting sealing members 70 and 72cooperate between cylindrical portion 32 and cylindrical portion 50 toimpede the escape of magnetically reactive medium 64. This type of“labyrinth” seal is effective to retain a magnetically reactive powderwithin gap 66. Sealing members 70 and 72 include cavities 74 and 76respectively. During application of a magnetic field when both rotatablemembers 30 and 40 are interlocked, centrifugal forces pull themagnetically reactive medium 64 in cavities 74 and 76 to the outersurface 77 of cavity 76 whereby the centrifugal forces and magnetic fluxpull the powder into gap 66. When no magnetic field is applied to device10, the magnetically reactive powder is allowed to disseminate intocavities 74 and 76, but is substantially prevented from exiting cavity74 due to the labyrinth geometry of the interacting sealing members 70and 72. Sealing member 72 further includes a cylindrical retainingportion 78 that cooperates with an annular seat 80 in second rotatablebody 40 to retain sealing member 72. Similar non-contacting annularsealing members 82 and 84 are fixedly attached to first rotatable member30 and second rotatable member 40 respectively. Sealing members 82 and84 cooperate to impede the escape of magnetically reactive medium 64 insubstantially the same manner as sealing members 70 and 72.

Magnetic particle device 10 further requires a source of magnetic flux,such as a magnet. As shown in FIGS. 1 and 4, a stationary toroidalelectromagnet 86 is mounted on the outside of housing member 12 betweenfirst rotatable member 30 an housing member 12. In the alternative, themagnetic source may be a permanent magnet 87 supplemented by acounteracting electromagnet 86, as shown in FIG. 1A, so that magneticparticle device 10 will default to being engaged should electromagnet 86fail. Also in the alternative, the magnetic source may be mounted onouter surface 54 of second rotatable member 40.

First rotatable member 30 and electromagnet 86 are not in contact, butdefine therebetween a uniform gap 88, generally toroidal inconfiguration. Electromagnet 86 includes a rigid shell 90, shown asbeing C-shaped in cross-section, opening to the outside of the toroidand having known magnetic properties. Rigid shell 90 is shown ascomprising two annular elements 92 and 94 joined by a plurality offasteners 96. In the alternative, rigid shell 90 could comprise a numberof annular elements cooperating to define the C-shaped geometry of therigid shell as seen in FIG. 5. Electromagnet 86 further includes atypical coil of conductive wire 98, application of an electric currentto the coil generating a known electromagnetic field in the vicinity ofelectromagnet 86. Electromagnet 86 is controlled by an electroniccontroller (not illustrated) designed to provide an electrical currentto the coil via wires 99 under predetermined conditions. The controllerprocesses all input, being sensor readings or operator selections, todetermine the appropriate current level needed by electromagnet 86 togenerate the magnetic field so that the magnetically reactive medium 64locks into chains to achieve the desired transfer of torque within thedevice 10.

FIG. 2 shows magnetically reactive medium 64 disposed in gap 66 withoutapplication of a magnetic field. In this state, no appreciable torque istransferred between first rotatable member 30 and second rotatablemember 40. Second rotatable member 40 is thus free to rotate relative tofirst rotatable member 30.

It is well known in the art that lines of magnetic flux 68 travel a pathsubstantially through structures with known magnetic properties. As seenin FIG. 4, upon application of a magnetic field in the vicinity ofelectromagnet 86, lines of magnetic flux 68 exit rigid shell 90 inelectromagnet 86 and traverse gap 88, whereby flux 68 saturates areas 95located radially inwardly of grooves 38 in first rotatable member 30.Upon saturation of areas 95, lines of magnetic flux 68 follow a path ofleast resistance and traverse gap 66, through working surfaces 93, intosecond rotatable member 40. The narrowest width of grooves 38 is bestdesigned to be greater than the width of gap 66 thus preventing flux 68from traversing grooves 38. Upon entry into second rotatable member 40,flux 68 saturates areas 97 located radially outwardly of grooves 56.Upon saturation of areas 97, flux 68 traverses gap 66 through workingsurfaces 58, into first rotatable member 30. The process of traversinggap 66 is repeated until the number of grooves 38 and 56 are exhausted.The flux path is completed as flux 68 traverses gap 66 and gap 88 andreenters rigid shell 90 of electromagnet 86.

As seen in FIG. 3, magnetically reactive particles 65 in magneticallyreactive medium 64 change formation, in relation to the intensity of themagnetic field, by aligning with the lines of magnetic flux 68 as flux68 traverses gap 66 through working surfaces 58. Magnetically reactiveparticles 65 under the influence of a magnetic field will lock intochains 100 increasing the shear force and creating a mechanical frictionagainst the working surfaces 58 facing gap 66. The increased shear forceand mechanical friction result in a corresponding transfer of torquebetween first member 30 and second member 40.

FIGS. 5 and 6 illustrate two variations of the embodiment of FIG. 1depicting a modified groove arrangement. Both embodiments operate in amanner substantially similar to the embodiment of FIG. 1. In bothembodiments, lines of magnetic flux 68 (not illustrated) generated byelectromagnet 86 first exit rigid shell 90 and travel a path across gap88 into first rotatable member 30. As seen in FIG. 5, upon entry intofirst rotatable member 30, flux 68 saturates areas 95 a. Uponsaturation, flux 68 follows the next path of least resistance andtraverses gap 66 into second rotatable member 40. As seen in FIG. 6,upon entry into first rotatable member 30, flux 68 saturates areas 95 b.Upon saturation, flux 68 follows the next path of least resistance andtraverses gap 66 into second rotatable member 40. The embodiments inFIGS. 5 and 6 differ from the embodiment of FIG. 1 in that the capacityto store magnetically reactive medium 64 in grooves 38 and 56 issubstantially or totally reduced, resulting in more medium 64 in gap 66.The increased amount of medium 64 in gap 66 increases the drag againstsecond rotatable member 40 as member 40 rotates about first rotatablemember 30 when the electromagnet is not energized.

FIG. 7 is a cross-sectional view of a fourth embodiment of the presentinvention. In this embodiment, the first rotatable member 30 and secondrotatable member 40 include non-continuous apertures 102 and 104respectively. Apertures 104 in second rotatable member 40 are positionedradially outwardly of a point equidistantly between apertures 102 infirst rotatable member 30. Lines of magnetic flux 68 (not illustrated)generated by electromagnet 86 first exit rigid shell 90 and travel apath across gap 88 into first rotatable member 30. Flux 68 then travelsa path of least resistance through a plurality of bridge portions 106(as seen in FIG. 8) located between apertures 102 until a level ofsaturation is reached. Upon saturation, flux 68 follows the next path ofleast resistance and traverses gap 66 into second rotatable member 40through working surfaces 93. Upon entry into second rotatable member 40,flux 68 saturates a plurality of bridge portions 108 (as seen in FIG. 8)located between apertures 104 until a level of saturation is reached.Provided the width of apertures 102 and 104 are greater than the widthof gap 66, lines of magnetic flux 68 traverse gap 66 through workingsurfaces 58. The process of traversing gap 66 is repeated until thenumber of apertures 102 and 104 is exhausted. The path is completed asflux 68 traverses gap 66 and gap 88 and reenters rigid shell 90 ofelectromagnet 86. In this embodiment, an annular sealing element 72 aincludes a cylindrical retaining portion 78 a that cooperates with aannular groove 80 a to retain annular sealing element 72 a. Cylindricalretaining portion 78 a further serves the purpose of inhibiting theescape of the magnetically reactive medium from apertures 104 in secondrotatable member 40. Similarly, a cylindrical retaining member 109 isfixedly attached to inner surface 34 of first rotatable member 30 andserves the purpose of inhibiting the escape of the magnetically reactivemedium from apertures 102 in first rotatable member 30.

FIG. 9 is a cross-sectional view of a fifth embodiment of the presentinvention. In this embodiment, the first rotatable member 30 and secondrotatable member 40 include a plurality of alternating continuousmagnetic rings 110 and continuous non-magnetic rings 112. Magnetic rings110 and non-magnetic rings 112 are secured to rotatable members 30 and40 by a plurality of fasteners 114, although the method of securingrings 110 and 112 is not intended to be limited thereto. The rings arepositioned such that non-magnetic rings 112 in second rotatable member40 are positioned radially outwardly of a point equidistantly betweennon-magnetic rings 112 in first rotatable member 30. Fasteners 114, likenon-magnetic rings 112, are preferred to be of a non-magnetic material,such as aluminum or stainless steel. Upon excitation of electromagnet86, lines of magnetic flux 68 (not illustrated) first exit rigid shell90 and follow a path of least resistance by traversing gap 88 into firstrotatable member 30. Upon entry into first rotatable member 30, thecontinuous non-magnetic rings 112 prevent flux 68 from short-circuitingthrough first rotatable member 30. Therefore, flux 68 follows a path ofleast resistance and traverses gap 66 through working surfaces 93 intosecond rotatable member 40. Upon entry into second rotatable member 40,flux 68 travels a path through second rotatable member 40 until flux 68encounters continuous non-magnetic ring 112 and is forced to traversegap 66 through working surfaces 58. The process of traversing gap 66 isrepeated until the number of continuous non-magnetic rings 112 isexhausted. The path is completed as flux 68 traverses gap 66 and gap 88and reenters rigid shell 90 of electromagnet 86.

The magnetic particle device 10 of present invention is a torquetransfer device in which portions of an input member 40 and an outputmember 30 are provided with regions of relatively high magneticpermeability and regions of relatively low magnetic permeability. Theseregions of relatively high and low magnetic permeability are positionedto form a flux path through which lines of magnetic flux, generallydenoted by element number 68, travel. As described above, the regions ofrelatively low magnetic permeability are formed by introducingnon-magnetic materials, such as stainless steel, aluminum or a polymer,into input and output members 40, 30 or by removing material from inputand output members 40, 30 to form a cavity or groove. In the embodimentillustrated in FIG. 1, the regions of relatively low magneticpermeability include annular grooves located in input and output members40, 30. The grooves may be positioned in the inner or outer surfaces ofinput and output members 40, 30 or, alternatively, in both the inner andouter surfaces of the input and output members 40, 30. In the embodimentillustrated in FIG. 9, the regions of relatively low magneticpermeability include non-magnetic rings of metal such as stainlesssteel. In the embodiment illustrated in FIG. 7, the regions ofrelatively low magnetic permeability include circumferentiallyextending, non-continuous apertures located in input and output members40, 30.

The input and output members 40, 30 of magnetic particle device 10preferably include multiple regions of relatively high and low magneticpermeability. However, device 10 may be configured to include any numberof alternating regions of high and low magnetic permeability with themost basic configuration being at least one region of relatively lowmagnetic permeability in output member 30 and at least one region ofrelatively low magnetic permeability in input member 40. The at leastone region of relatively low magnetic permeability in output member 30is provided to prevent lines of magnetic flux 68 from “short-circuiting”through output member 30.

In operation, the traversing lines of magnetic flux 68 activatemagnetically reactive medium 64. The magnetically reactive particles 65in medium 64 change formation, in relation to the intensity of themagnetic field, by aligning with lines of magnetic flux 68 as flux 68traverses gap 66. Magnetically reactive particles 65 under the influenceof a magnetic field will lock into chains 100 increasing the shear forceand creating a mechanical friction against input member 40 and outputmember 30. The increased shear force and mechanical friction results ina corresponding transfer of torque between input member 40 and outputmember 30 that is precisely controlled in relation to the strength ofthe applied magnetic field.

As will be appreciated, the present invention can transfer a givenamount of torque between input and output members 40, 30 with a weakermagnetic field due to the greater amount of activated medium 64. Thus,increasing the number of regions of relatively high and low magneticpermeability permits the use of a smaller source of magnetic flux toprovide, inter alia, a substantial weight savings over conventionaltorque transferring devices.

The present invention has been particularly shown and described withreference to the foregoing embodiments, which are merely illustrative ofthe best modes for carrying out the invention. It should be understoodby those skilled in the art that various alternatives to the embodimentsof the invention described herein may be employed in practicing theinvention without departing from the spirit and scope of the inventionas defined in the following claims. It is intended that the followingclaims define the scope of the invention and that the method andapparatus within the scope of these claims and their equivalents becovered thereby. This description of the invention should be understoodto include all novel and non-obvious combinations of elements describedherein, and claims may be presented in this or a later application toany novel and non-obvious combination of these elements. Moreover, theforegoing embodiments are illustrative, and no single feature or elementis essential to all possible combinations that may be claimed in this ora later application.

1. A torque transfer device, comprising: an input member for receivingtorque from an external source, said input member having at least oneregion of relatively high magnetic permeability and at least one regionof relatively low magnetic permeability; an output member disposedradially inward of said input member to define a torque transferringregion therebetween, said output member having at least one region ofrelatively high magnetic permeability and at least one region ofrelatively low magnetic permeability; a source of magnetic flux; andwherein said magnetic flux is forced to travel a weaving pathsubstantially between said regions of relatively low magneticpermeability, traversing said torque transferring region to activatesaid torque transferring region and permit transfer of torque betweensaid input and output members.
 2. The torque transfer device of claim 1,wherein said torque transferring region is defined by a gap containing amagnetically reactive medium.
 3. The torque transfer device of claim 1,wherein said source of magnetic flux includes an electromagnet.
 4. Thetorque transfer device of claim 3, wherein said source of magnetic fluxincludes a permanent magnet.
 5. The torque transfer device of claim 4,wherein said permanent magnet is supplemented by said electromagnet. 6.The torque transfer device of claim 1, wherein said regions ofrelatively low magnetic permeability include a non-magnetic ring.
 7. Thetorque transfer device of claim 1, wherein said regions of relativelylow magnetic permeability include a groove.
 8. The torque transferdevice of claim 1, wherein said regions of relatively low magneticpermeability include an aperture.
 9. The torque transfer device of claim1, wherein said regions of relatively low magnetic permeability includeat least one of a non-magnetic ring, a groove and an aperture.
 10. Thetorque transfer device of claim 1, wherein the source of magnet flux isselectively controllable to provide a variable level of magnetic flux.11. A magnetic particle device comprising: a stationary housing memberhaving a duct therethrough for receiving a rotatable shaft, saidrotatable shaft having a first rotatable member mounted thereon; asecond rotatable member positioned radially outwardly of said firstrotatable member, said first and second rotatable members cooperating todefine a gap therebetween, said gap containing a magnetically reactivemedium; a source of magnetic flux; said first rotatable member and saidsecond rotatable member including regions of relatively high and lowmagnetic permeability, said regions of relatively low magneticpermeability positioned to create a working surface therebetween; andwherein said magnetic flux is forced to travel a weaving pathsubstantially between said regions of relatively low magneticpermeability, traversing said gap substantially through said workingsurface so as to magnetize said magnetically reactive medium andtransform said magnetically reactive medium into a torque transmittingcoupling to permit the transfer of torque between said first and secondrotatable members.